Love as an assignment
Right away, we see the novel as an expression of irony. Situational irony reigns supreme for the Japanese mail-order brides who are willing to undertake an exercise in love and commitment for a chance at a better life. Their choice is to use their sexual availability as a resource, promising love and marriage to a stranger. In this manner, their natural desire for romance becomes an assignment as they try to make the best of (typically unpleasant) situations. Their first task is the hardest; forgiving a stranger for lying to them.
The lying husbands
The husbands are ironic because they have an opportunity to make a nice relationship with these brides who are genuinely ethical and hard-working gals. Instead, most of the men use the opportunity to mislead their new wives, underscoring the major irony of sexual selection and mating—humans naturally work to entice impressive mates, which means that romance naturally implies levels of deception, which is contrary to the success of the relationship. The husbands represent an ironic compromise that dooms their marriages to failure. Also ironic is this: The husbands sort of assume that by importing wives, they will somehow have automatically-easier marriages, which is obviously just Oedipal wish-fulfillment. That objectifies the women in their own marriage.
The preference for rural life
Once the girls get a taste of the "good life," they (a lot of them) quickly desire a harder life. They want a rural community with long workdays spent with company and community. Then, their lives would align more naturally with the ethical virtues of Japanese culture. See, the girls encounter a reality which is ironic in a situational way, in their opinion, because they see that life is clearly better lived in a more tight-knit, open-minded community, but those are not the virtues that define life in California. Californian city life is often fiercely individualistic, and the women don't understand why people would live lives so detached from their nature. By abandoning their homes in favor of hard lives on farms, they prove their unique point of view.
The irony of xenophobia
When Pearl Harbor occurs, the world suddenly seems too small. The nation of Japan seems to lurk along the whole West Coast, because after all, the Japanese attacked the US once, and California would be their second-closest target behind Pearl Harbor. This paranoia is amplified by racism against Asian people in Western America, and therefore, the nation responds severely to a threat that is not real. When the Japanese people are punished for the attack on Pearl Harbor, the irony of xenophobia is made clear. It simply does not follow that foreigners would be particularly dangerous, but paranoia makes that a tempting conclusion.
The internment camps
Life in the internment camps is defined by dramatic irony. The cast of characters all converge in a government machine which strips them of their individuality, treating anyone who looks Japanese as a potential enemy of the state. The camps are severely chaotic for the Japanese people, therefore, because they do not have the promise of legal protection; it is the highest authority of the land which has chosen to completely disenfranchise them. Their experience of the future from within the camps is one of pure speculation, colored by the absolute horror of government conspiracy and the threat of death looming each day that passes.
